Note: Be sensitive to your cat when relocating her litter box. Wouldn't it stress you out if you didn't know where your toilet was when you needed it? Make necessary changes gradually, and only if your cat seems comfortable with them.
2. Make the entire bathroom inaccessible to your dog and put the litter box there.
Install a baby gate high enough off the ground that your cat can slip underneath, but not your dog. Or - if you have a small dog (and an agile cat) - set up a landing so your cat can comfortably jump the gate. Carpeted kitty furniture on either side is ideal.